The present invention relates generally to satellite command systems and methods, and more particularly, to a satellite command system and method that provides satellite commanding using remotely-controlled modulation of satellite on-board telemetry parameters.
The assignee of the present invention manufactures and deploys communication satellites that orbit the Earth. Typically, the satellites contains a plurality of central processing units (CPUs). It is possible that a failure may occur while a satellite is in orbit that renders one of the CPU""s normal command pathways unusable. In the past, in the event of such a normal command pathway failure, the affected CPU could not be used. There is a need for a solution to this possible problem.
The present invention provides for a satellite command system and method that provides satellite commanding using remotely-controlled modulation of satellite on-board telemetry parameters. The present invention is useful after a failure of the normal on-board command pathway, wherein command information flows from command receivers to bit detectors, to command decoders, and finally to a computer (CPU). The present invention creates alternate command pathways through novel use of the basic spacecraft control electronics (SCE) architecture already on board the satellite. The present invention does not require any equipment specifically dedicated to this task.
The basic spacecraft control electronics already performs the task of gathering data from equipment distributed over the spacecraft for telemetry. The crux of the present invention is to cause the CPU to interpret certain patterns of variation of telemetry quantities over time as command information. To link ground controllers with the satellite, the particular telemetry item used must be manipulatable from the ground. Equipment that is sensitive to RF waves is most convenient for this purpose.
In an exemplary command system and method, the particular on-board telemetry parameters used happened to be associated with command input equipment but the traditional command input capability of that equipment was not operative. The satellite has a plurality of redundant processor units that are coupled to the command input equipment by way of a respective plurality of buses and command input buses that provide redundant command pathways to each of the redundant processor units. The redundant processor units respectively process the received commands transferred to them by way of the respective bus controllers and buses to control the satellite. The redundant processor units are also coupled to a plurality of distributed data collection units. The distributed data collection units perform command distribution and telemetry data collection.
The system and method of the present invention bypass the presence of a hardware failure that affects the command pathway of the processor units. Software is provided on each of the redundant processor units that creates separate DMA command pathways between each of the redundant processor units and the distributed data collection units.
To use the novel command pathway, a command translator is used at a ground station to translate a command that is to be implemented on the satellite into a form ready for modulation. The translated command is then superimposed on a signal that will be measured as telemetry data on-board the satellite. Thus, the command is generated and modulated on the ground to produce data that is available to the CPU through its telemetry collection functions.
Software implemented in processor units recognizes the modulation, and processes it to reconstruct the command. The processor unit then executes the command. Each of the redundant processor units can thus process the commands received to control the satellite.
The satellite command links, primary or redundant, are replicated without requiring additional, or any, dedicated satellite on-board RF command link receiving hardware. The present invention thus increases satellite command pathway redundancy and thereby improves satellite reliability, without any added costs in mass, power, or on-board hardware.
The present invention was developed, and a specific satellite design change was implemented, in response to an in-orbit failure involving one of an orbiting satellite""s two main on-board MIL-STD-1750 central processing units (CPUs). The failure rendered the affected CPU""s normal command input programmed input/output (PIO) bus unusable, while that CPU""s direct memory access (DMA) input/output capabilities, including its MIL-STD-1553 data bus, were still fully functional.
The in-orbit failure was corrected using the present invention. In particular, using the present invention, virtually all command link capability was restored to the in-orbit failed main central processing unit, including command link pathway redundancy.